Engine hood for motor vehicles for the protection of pedestrians

Abstract

An engine hood for motor vehicles possesses a deformable head impact zone for the protection of pedestrians in the event of a collision with the motor vehicle. The engine hood is composed of two or more load-bearing shells and has a flexural strength profile which is low adjacent the edges and increases continuously toward the middle of the hood. At the same time, the engine hood has a uniform mass distribution ovcr the entire surface. Consequently, irrespective of the position the engine hood, the same characteristic for the head impact is achieved everywhere. The advantageous embodiment of the engine hood provides a reinforcing panel with regularly arranged beads, at most three beads forming a junction point so as to reduce local rigidities.

1. An engine hood for a motor vehicle having a body, the engine hood having a deformable head impact zone for the protection of pedestrians in the event of a collision with the motor vehicle and comprising an outer shell and an inner shell, the engine hood being supported relative to the body at bearer regions adjacent at least two opposite edge regions of the engine hood, wherein the engine hood has a flexural strength profile in the head impact zone, the flexural strength profile varying over both a longitudinal dimension and a lateral dimension of the engine hood according to the following:
 adjacent the bearer regions, a flexural strength predominantly lower than or equal to a first value;  
 in a middle region of the engine hood, a flexural strength predominantly higher than or equal to a second value, the second value being greater than the first value; and  
 in intermediate regions between the bearer regions and the middle region, a flexural strength predominantly higher than the first value and lower than the second value.  
 
     
     
       2. The engine hood as claimed in  claim 1 , wherein the outer shell has a first thickness and the inner shell has a second thickness, a sum of the first and second thicknesses in the head impact zone having a value profile according to the following:
 adjacent the bearer regions predominantly lower than or equal to a first thickness;  
 in a middle region, predominantly higher than or equal to a second thickness, the second thickness being greater than the first thickness; and  
 in intermediate regions between the bearer regions and the middle region, predominantly higher than the first thickness and lower than the second thickness.  
 
     
     
       3. The engine hood as claimed in  claim 2 , wherein, in the region of the bead impact zone, the sum of the shell thicknesses has a generally continuous and rising profile from the bearers to the edges and from the edges to the middle. 
     
     
       4. The engine hood as claimed in  claim 1 , wherein a distance separates the outer shell and inner shell, the distance varying in the region of the head impact zone in accordance with the following:
 adjacent the bearer regions, the distance is predominantly lower than or equal to a first distance;  
 in a middle region, the distance is predominantly higher than or equal to a second distance, the second distance being greater than the first distance; and  
 in intermediate regions between the bearer regions and the middle region, the distance is predominantly higher than the first distance and lower than the second distance.  
 
     
     
       5. The engine hood as claimed in  claim 4 , wherein, in the region of the head impact zone, the distance between the outer shell and the inner shell has a generally continuous and rising profile from the bearers to the edges and from the edges to the middle. 
     
     
       6. The engine hood as claimed in  claim 1 , wherein at least one of the shells is formed of a material having a modulus of elasticity that varies in the head impact zone according to the following:
 adjacent the bearer regions, predominantly lower than or equal to a first modulus of elasticity;  
 in a middle region, predominantly higher than or equal to a second modulus of elasticity, a second modulus of elasticity being greater than the first modulus of elasticity; and  
 in intermediate regions between the bearer regions and the middle region, predominantly higher than the first modulus of elasticity and lower than the second modulus of elasticity.  
 
     
     
       7. The engine hood as claimed in  claim 6 , wherein, in the region of the head impact zone, the modulus of elasticity of the shell material has a generally continuous and rising profile from the bearers to the edges and from the edges to the middle. 
     
     
       8. The engine hood as claimed in  claim 1 , wherein the inner shell has beads which are connected to the outer shell at bead flanges bearing against the outer shell, and the flexural strength of each bead between two junction points is determined, in the region of the head impact zone, from the dimensions of the bead and of the outer shell at a section perpendicular to a neutral axis of the bead between the two junction points. 
     
     
       9. The engine hood as claimed in  claim 8 , wherein the beads have the following widths in the region of the head impact zone:
 adjacent the bearer regions, predominantly lower than or equal to a first width;  
 in a middle region predominantly higher than or equal to a second width, the second width being greater than the first width; and  
 in intermediate regions between the bearer regions and the middle region, predominantly higher than the first width and lower than the second width.  
 
     
     
       10. The engine hood as claimed in  claim 9 , wherein, in the region of the head impact zone, the width of the beads has a generally continuous and rising profile from the bearers to the edges and from the edges to the middle. 
     
     
       11. The engine hood as claimed in  claim 8 , wherein, in the region of the head impact zone, the beads are shaped as hat profiles and the junctions of the beads are formed predominantly by three hat profiles converging with one another. 
     
     
       12. The engine hood as claimed in  claim 1 , wherein, in the region of the head impact zone, the flexural strength of the engine hood has a generally continuous and rising profile from the bearers to the edges and from the edges to the middle. 
     
     
       13. The engine hood as claimed in  claim 1 , wherein at least one intermediate supporting shell is disposed between the outer shell and the inner shell. 
     
     
       14. The engine hood as claimed in  claim 13 , wherein the supporting shell has the following different densities:
 adjacent a bearer portion predominantly lower than or equal to a first density;  
 adjacent a middle region predominantly higher than or equal to a second density, the second density being greater than the first density; and  
 in intermediate regions between the bearer regions and the middle region, predominantly higher than the first density and lower than the second density.  
 
     
     
       15. The engine hood as claimed in  claim 1 , wherein the engine hood without bearers has an approximately uniform mass distribution such that all reference surface elements that may be defined on the engine hood in the head impact zone, with the exception of the bearer regions, have essentially identical weights per unit area, with a permissible deviation from an average weight per unit area of the engine hood without bearers of not over 20%.